Rammig in steel pipes, for instance protective or supply pipes, by means of a percussion boring device or a rammer of which the conical impact head engages, either directly or via an attachment, in the rear end of a pipe guided on supporting blocks with a cutting shoe that engages over the leading end on both the inside and the outside, has increasingly come to be used in practice. In most cases the full length of the pipe is not driven in in one piece, but short pieces, whose length depends on the size of the excavation available for preparing them for ramming in, are driven in in sucession. Each time this is done the follower pipe has to be connected by welding to the pipe or string of pipe lengths that has already been buried in the ground.
This series of operations is repeated until the complete pipe string length has been built up. Welding the individual pipe joints has however been found to involve problems in that the pipes have to be welded to one another in the starting pit around their entire circumferences in a leak-proof and impact-resistant manner. The welding thus requires qualified pipe line welders, particularly because the pipe joints have also to be welded on their undersides with the same quality. To enable the welding on the underside to be performed at least under improved conditions the starting pit is made deeper in this region. Since it is still not possible to see the welding point directly under the pipe, the welding also requires the use of a welding mirror.